/*
 * Copyright (c) 1999-2010 Apple Inc.  All Rights Reserved.
 *
 * @APPLE_LICENSE_HEADER_START@
 *
 * This file contains Original Code and/or Modifications of Original Code
 * as defined in and that are subject to the Apple Public Source License
 * Version 2.0 (the 'License'). You may not use this file except in
 * compliance with the License. Please obtain a copy of the License at
 * http://www.opensource.apple.com/apsl/ and read it before using this
 * file.
 *
 * The Original Code and all software distributed under the License are
 * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
 * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
 * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
 * Please see the License for the specific language governing rights and
 * limitations under the License.
 *
 * @APPLE_LICENSE_HEADER_END@
 */
#ifndef _MACHO_LOADER_H_
#define _MACHO_LOADER_H_

/*
 * This file describes the format of mach object files.
 */

/*
 * The 32-bit mach header appears at the very beginning of the object file for
 * 32-bit architectures.
 */
struct mach_header {
  uint32_t magic;               /* mach magic number identifier */
  cpu_type_t cputype;           /* cpu specifier */
  cpu_subtype_t cpusubtype;     /* machine specifier */
  uint32_t filetype;            /* type of file */
  uint32_t ncmds;               /* number of load commands */
  uint32_t sizeofcmds;          /* the size of all the load commands */
  uint32_t flags;               /* flags */
};

/* Constant for the magic field of the mach_header (32-bit architectures) */
#define  MH_MAGIC  0xfeedface  /* the mach magic number */
#define MH_CIGAM  0xcefaedfe  /* NXSwapInt(MH_MAGIC) */

/*
 * The 64-bit mach header appears at the very beginning of object files for
 * 64-bit architectures.
 */
struct mach_header_64 {
  uint32_t magic;               /* mach magic number identifier */
  cpu_type_t cputype;           /* cpu specifier */
  cpu_subtype_t cpusubtype;     /* machine specifier */
  uint32_t filetype;            /* type of file */
  uint32_t ncmds;               /* number of load commands */
  uint32_t sizeofcmds;          /* the size of all the load commands */
  uint32_t flags;               /* flags */
  uint32_t reserved;            /* reserved */
};

/* Constant for the magic field of the mach_header_64 (64-bit architectures) */
#define MH_MAGIC_64 0xfeedfacf  /* the 64-bit mach magic number */
#define MH_CIGAM_64 0xcffaedfe  /* NXSwapInt(MH_MAGIC_64) */

/*
 * The layout of the file depends on the filetype.  For all but the MH_OBJECT
 * file type the segments are padded out and aligned on a segment alignment
 * boundary for efficient demand pageing.  The MH_EXECUTE, MH_FVMLIB, MH_DYLIB,
 * MH_DYLINKER and MH_BUNDLE file types also have the headers included as part
 * of their first segment.
 *
 * The file type MH_OBJECT is a compact format intended as output of the
 * assembler and input (and possibly output) of the link editor (the .o
 * format).  All sections are in one unnamed segment with no segment padding.
 * This format is used as an executable format when the file is so small the
 * segment padding greatly increases its size.
 *
 * The file type MH_PRELOAD is an executable format intended for things that
 * are not executed under the kernel (proms, stand alones, kernels, etc).  The
 * format can be executed under the kernel but may demand paged it and not
 * preload it before execution.
 *
 * A core file is in MH_CORE format and can be any in an arbritray legal
 * Mach-O file.
 *
 * Constants for the filetype field of the mach_header
 */
#define  MH_OBJECT  0x1 /* relocatable object file */
#define  MH_EXECUTE  0x2 /* demand paged executable file */
#define  MH_FVMLIB  0x3 /* fixed VM shared library file */
#define  MH_CORE    0x4 /* core file */
#define  MH_PRELOAD  0x5 /* preloaded executable file */
#define  MH_DYLIB  0x6 /* dynamically bound shared library */
#define  MH_DYLINKER  0x7 /* dynamic link editor */
#define  MH_BUNDLE  0x8 /* dynamically bound bundle file */
#define  MH_DYLIB_STUB  0x9 /* shared library stub for static */

/*  linking only, no section contents */
#define  MH_DSYM    0xa /* companion file with only debug */

/*  sections */
#define  MH_KEXT_BUNDLE  0xb /* x86_64 kexts */

/* Constants for the flags field of the mach_header */
#define  MH_NOUNDEFS  0x1 /* the object file has no undefined
                           references */
#define  MH_INCRLINK  0x2 /* the object file is the output of an
                           incremental link against a base file
                           and can't be link edited again */
#define MH_DYLDLINK  0x4 /* the object file is input for the
                           dynamic linker and can't be staticly
                           link edited again */
#define MH_BINDATLOAD  0x8 /* the object file's undefined
                             references are bound by the dynamic
                             linker when loaded. */
#define MH_PREBOUND  0x10  /* the file has its dynamic undefined
                             references prebound. */
#define MH_SPLIT_SEGS  0x20  /* the file has its read-only and
                               read-write segments split */
#define MH_LAZY_INIT  0x40  /* the shared library init routine is
                               to be run lazily via catching memory
                               faults to its writeable segments
                               (obsolete) */
#define MH_TWOLEVEL  0x80  /* the image is using two-level name
                             space bindings */
#define MH_FORCE_FLAT  0x100 /* the executable is forcing all images
                               to use flat name space bindings */
#define MH_NOMULTIDEFS  0x200 /* this umbrella guarantees no multiple
                                 defintions of symbols in its
                                 sub-images so the two-level namespace
                                 hints can always be used. */
#define MH_NOFIXPREBINDING 0x400  /* do not have dyld notify the
                                     prebinding agent about this
                                     executable */
#define MH_PREBINDABLE  0x800 /* the binary is not prebound but can
                                 have its prebinding redone. only used
                                 when MH_PREBOUND is not set. */
#define MH_ALLMODSBOUND 0x1000  /* indicates that this binary binds to
                                   all two-level namespace modules of
                                   its dependent libraries. only used
                                   when MH_PREBINDABLE and MH_TWOLEVEL
                                   are both set. */
#define MH_SUBSECTIONS_VIA_SYMBOLS 0x2000 /* safe to divide up the sections into
                                             sub-sections via symbols for dead
                                             code stripping */
#define MH_CANONICAL    0x4000  /* the binary has been canonicalized
                                   via the unprebind operation */
#define MH_WEAK_DEFINES  0x8000  /* the final linked image contains
                                   external weak symbols */
#define MH_BINDS_TO_WEAK 0x10000  /* the final linked image uses
                                     weak symbols */

#define MH_ALLOW_STACK_EXECUTION 0x20000  /* When this bit is set, all stacks
                                             in the task will be given stack
                                             execution privilege.  Only used in
                                             MH_EXECUTE filetypes. */
#define MH_ROOT_SAFE 0x40000  /* When this bit is set, the binary
                                 declares it is safe for use in
                                 processes with uid zero */

#define MH_SETUID_SAFE 0x80000  /* When this bit is set, the binary
                                   declares it is safe for use in
                                   processes when issetugid() is true */

#define MH_NO_REEXPORTED_DYLIBS 0x100000  /* When this bit is set on a dylib,
                                             the static linker does not need to
                                             examine dependent dylibs to see
                                             if any are re-exported */
#define  MH_PIE 0x200000 /* When this bit is set, the OS will
                           load the main executable at a
                           random address.  Only used in
                           MH_EXECUTE filetypes. */
#define  MH_DEAD_STRIPPABLE_DYLIB 0x400000 /* Only for use on dylibs.  When
                                             linking against a dylib that
                                             has this bit set, the static linker
                                             will automatically not create a
                                             LC_LOAD_DYLIB load command to the
                                             dylib if no symbols are being
                                             referenced from the dylib. */
#define MH_HAS_TLV_DESCRIPTORS 0x800000 /* Contains a section of type
                                           S_THREAD_LOCAL_VARIABLES */

#define MH_NO_HEAP_EXECUTION 0x1000000  /* When this bit is set, the OS will
                                           run the main executable with
                                           a non-executable heap even on
                                           platforms (e.g. i386) that don't
                                           require it. Only used in MH_EXECUTE
                                           filetypes. */

/*
 * The load commands directly follow the mach_header.  The total size of all
 * of the commands is given by the sizeofcmds field in the mach_header.  All
 * load commands must have as their first two fields cmd and cmdsize.  The cmd
 * field is filled in with a constant for that command type.  Each command type
 * has a structure specifically for it.  The cmdsize field is the size in bytes
 * of the particular load command structure plus anything that follows it that
 * is a part of the load command (i.e. section structures, strings, etc.).  To
 * advance to the next load command the cmdsize can be added to the offset or
 * pointer of the current load command.  The cmdsize for 32-bit architectures
 * MUST be a multiple of 4 bytes and for 64-bit architectures MUST be a multiple
 * of 8 bytes (these are forever the maximum alignment of any load commands).
 * The padded bytes must be zero.  All tables in the object file must also
 * follow these rules so the file can be memory mapped.  Otherwise the pointers
 * to these tables will not work well or at all on some machines.  With all
 * padding zeroed like objects will compare byte for byte.
 */
struct load_command {
  uint32_t cmd;                 /* type of load command */
  uint32_t cmdsize;             /* total size of command in bytes */
};

/*
 * After MacOS X 10.1 when a new load command is added that is required to be
 * understood by the dynamic linker for the image to execute properly the
 * LC_REQ_DYLD bit will be or'ed into the load command constant.  If the dynamic
 * linker sees such a load command it it does not understand will issue a
 * "unknown load command required for execution" error and refuse to use the
 * image.  Other load commands without this bit that are not understood will
 * simply be ignored.
 */
#define LC_REQ_DYLD 0x80000000

/* Constants for the cmd field of all load commands, the type */
#define  LC_SEGMENT  0x1 /* segment of this file to be mapped */
#define  LC_SYMTAB  0x2 /* link-edit stab symbol table info */
#define  LC_SYMSEG  0x3 /* link-edit gdb symbol table info (obsolete) */
#define  LC_THREAD  0x4 /* thread */
#define  LC_UNIXTHREAD  0x5 /* unix thread (includes a stack) */
#define  LC_LOADFVMLIB  0x6 /* load a specified fixed VM shared library */
#define  LC_IDFVMLIB  0x7 /* fixed VM shared library identification */
#define  LC_IDENT  0x8 /* object identification info (obsolete) */
#define LC_FVMFILE  0x9 /* fixed VM file inclusion (internal use) */
#define LC_PREPAGE      0xa /* prepage command (internal use) */
#define  LC_DYSYMTAB  0xb /* dynamic link-edit symbol table info */
#define  LC_LOAD_DYLIB  0xc /* load a dynamically linked shared library */
#define  LC_ID_DYLIB  0xd /* dynamically linked shared lib ident */
#define LC_LOAD_DYLINKER 0xe  /* load a dynamic linker */
#define LC_ID_DYLINKER  0xf /* dynamic linker identification */
#define  LC_PREBOUND_DYLIB 0x10  /* modules prebound for a dynamically */

/*  linked shared library */
#define  LC_ROUTINES  0x11  /* image routines */
#define  LC_SUB_FRAMEWORK 0x12 /* sub framework */
#define  LC_SUB_UMBRELLA 0x13  /* sub umbrella */
#define  LC_SUB_CLIENT  0x14  /* sub client */
#define  LC_SUB_LIBRARY  0x15  /* sub library */
#define  LC_TWOLEVEL_HINTS 0x16  /* two-level namespace lookup hints */
#define  LC_PREBIND_CKSUM  0x17  /* prebind checksum */

/*
 * load a dynamically linked shared library that is allowed to be missing
 * (all symbols are weak imported).
 */
#define  LC_LOAD_WEAK_DYLIB (0x18 | LC_REQ_DYLD)

#define  LC_SEGMENT_64  0x19  /* 64-bit segment of this file to be
                               mapped */
#define  LC_ROUTINES_64  0x1a  /* 64-bit image routines */
#define LC_UUID    0x1b  /* the uuid */
#define LC_RPATH       (0x1c | LC_REQ_DYLD) /* runpath additions */
#define LC_CODE_SIGNATURE 0x1d  /* local of code signature */
#define LC_SEGMENT_SPLIT_INFO 0x1e  /* local of info to split segments */
#define LC_REEXPORT_DYLIB (0x1f | LC_REQ_DYLD)  /* load and re-export dylib */
#define  LC_LAZY_LOAD_DYLIB 0x20 /* delay load of dylib until first use */
#define  LC_ENCRYPTION_INFO 0x21 /* encrypted segment information */
#define  LC_DYLD_INFO   0x22  /* compressed dyld information */
#define  LC_DYLD_INFO_ONLY (0x22|LC_REQ_DYLD)  /* compressed dyld information only */
#define  LC_LOAD_UPWARD_DYLIB (0x23 | LC_REQ_DYLD) /* load upward dylib */
#define LC_VERSION_MIN_MACOSX 0x24  /* build for MacOSX min OS version */
#define LC_VERSION_MIN_IPHONEOS 0x25  /* build for iPhoneOS min OS version */
#define LC_FUNCTION_STARTS 0x26 /* compressed table of function start addresses */
#define LC_DYLD_ENVIRONMENT 0x27  /* string for dyld to treat
                                     like environment variable */
#define LC_MAIN (0x28|LC_REQ_DYLD)  /* replacement for LC_UNIXTHREAD */
#define LC_DATA_IN_CODE 0x29  /* table of non-instructions in __text */
#define LC_SOURCE_VERSION 0x2A  /* source version used to build binary */
#define LC_DYLIB_CODE_SIGN_DRS 0x2B /* Code signing DRs copied from linked dylibs */

/*
 * A variable length string in a load command is represented by an lc_str
 * union.  The strings are stored just after the load command structure and
 * the offset is from the start of the load command structure.  The size
 * of the string is reflected in the cmdsize field of the load command.
 * Once again any padded bytes to bring the cmdsize field to a multiple
 * of 4 bytes must be zero.
 */
union lc_str {
  uint32_t offset;              /* offset to the string */
#ifndef __LP64__
  char *ptr;                    /* pointer to the string */
#endif
};

/*
 * The segment load command indicates that a part of this file is to be
 * mapped into the task's address space.  The size of this segment in memory,
 * vmsize, maybe equal to or larger than the amount to map from this file,
 * filesize.  The file is mapped starting at fileoff to the beginning of
 * the segment in memory, vmaddr.  The rest of the memory of the segment,
 * if any, is allocated zero fill on demand.  The segment's maximum virtual
 * memory protection and initial virtual memory protection are specified
 * by the maxprot and initprot fields.  If the segment has sections then the
 * section structures directly follow the segment command and their size is
 * reflected in cmdsize.
 */
struct segment_command {        /* for 32-bit architectures */
  uint32_t cmd;                 /* LC_SEGMENT */
  uint32_t cmdsize;             /* includes sizeof section structs */
  char segname[16];             /* segment name */
  uint32_t vmaddr;              /* memory address of this segment */
  uint32_t vmsize;              /* memory size of this segment */
  uint32_t fileoff;             /* file offset of this segment */
  uint32_t filesize;            /* amount to map from the file */
  vm_prot_t maxprot;            /* maximum VM protection */
  vm_prot_t initprot;           /* initial VM protection */
  uint32_t nsects;              /* number of sections in segment */
  uint32_t flags;               /* flags */
};

/*
 * The 64-bit segment load command indicates that a part of this file is to be
 * mapped into a 64-bit task's address space.  If the 64-bit segment has
 * sections then section_64 structures directly follow the 64-bit segment
 * command and their size is reflected in cmdsize.
 */
struct segment_command_64 {     /* for 64-bit architectures */
  uint32_t cmd;                 /* LC_SEGMENT_64 */
  uint32_t cmdsize;             /* includes sizeof section_64 structs */
  char segname[16];             /* segment name */
  uint64_t vmaddr;              /* memory address of this segment */
  uint64_t vmsize;              /* memory size of this segment */
  uint64_t fileoff;             /* file offset of this segment */
  uint64_t filesize;            /* amount to map from the file */
  vm_prot_t maxprot;            /* maximum VM protection */
  vm_prot_t initprot;           /* initial VM protection */
  uint32_t nsects;              /* number of sections in segment */
  uint32_t flags;               /* flags */
};

/* Constants for the flags field of the segment_command */
#define  SG_HIGHVM  0x1 /* the file contents for this segment is for
                         the high part of the VM space, the low part
                         is zero filled (for stacks in core files) */
#define  SG_FVMLIB  0x2 /* this segment is the VM that is allocated by
                         a fixed VM library, for overlap checking in
                         the link editor */
#define  SG_NORELOC  0x4 /* this segment has nothing that was relocated
                           in it and nothing relocated to it, that is
                           it maybe safely replaced without relocation */
#define SG_PROTECTED_VERSION_1  0x8 /* This segment is protected.  If the
                                       segment starts at file offset 0, the
                                       first page of the segment is not
                                       protected.  All other pages of the
                                       segment are protected. */

/*
 * A segment is made up of zero or more sections.  Non-MH_OBJECT files have
 * all of their segments with the proper sections in each, and padded to the
 * specified segment alignment when produced by the link editor.  The first
 * segment of a MH_EXECUTE and MH_FVMLIB format file contains the mach_header
 * and load commands of the object file before its first section.  The zero
 * fill sections are always last in their segment (in all formats).  This
 * allows the zeroed segment padding to be mapped into memory where zero fill
 * sections might be. The gigabyte zero fill sections, those with the section
 * type S_GB_ZEROFILL, can only be in a segment with sections of this type.
 * These segments are then placed after all other segments.
 *
 * The MH_OBJECT format has all of its sections in one segment for
 * compactness.  There is no padding to a specified segment boundary and the
 * mach_header and load commands are not part of the segment.
 *
 * Sections with the same section name, sectname, going into the same segment,
 * segname, are combined by the link editor.  The resulting section is aligned
 * to the maximum alignment of the combined sections and is the new section's
 * alignment.  The combined sections are aligned to their original alignment in
 * the combined section.  Any padded bytes to get the specified alignment are
 * zeroed.
 *
 * The format of the relocation entries referenced by the reloff and nreloc
 * fields of the section structure for mach object files is described in the
 * header file <reloc.h>.
 */
struct section {                /* for 32-bit architectures */
  char sectname[16];            /* name of this section */
  char segname[16];             /* segment this section goes in */
  uint32_t addr;                /* memory address of this section */
  uint32_t size;                /* size in bytes of this section */
  uint32_t offset;              /* file offset of this section */
  uint32_t align;               /* section alignment (power of 2) */
  uint32_t reloff;              /* file offset of relocation entries */
  uint32_t nreloc;              /* number of relocation entries */
  uint32_t flags;               /* flags (section type and attributes) */
  uint32_t reserved1;           /* reserved (for offset or index) */
  uint32_t reserved2;           /* reserved (for count or sizeof) */
};

struct section_64 {             /* for 64-bit architectures */
  char sectname[16];            /* name of this section */
  char segname[16];             /* segment this section goes in */
  uint64_t addr;                /* memory address of this section */
  uint64_t size;                /* size in bytes of this section */
  uint32_t offset;              /* file offset of this section */
  uint32_t align;               /* section alignment (power of 2) */
  uint32_t reloff;              /* file offset of relocation entries */
  uint32_t nreloc;              /* number of relocation entries */
  uint32_t flags;               /* flags (section type and attributes) */
  uint32_t reserved1;           /* reserved (for offset or index) */
  uint32_t reserved2;           /* reserved (for count or sizeof) */
  uint32_t reserved3;           /* reserved */
};

/*
 * The flags field of a section structure is separated into two parts a section
 * type and section attributes.  The section types are mutually exclusive (it
 * can only have one type) but the section attributes are not (it may have more
 * than one attribute).
 */
#define SECTION_TYPE     0x000000ff /* 256 section types */
#define SECTION_ATTRIBUTES   0xffffff00 /*  24 section attributes */

/* Constants for the type of a section */
#define  S_REGULAR    0x0 /* regular section */
#define  S_ZEROFILL    0x1 /* zero fill on demand section */
#define  S_CSTRING_LITERALS  0x2 /* section with only literal C strings */
#define  S_4BYTE_LITERALS  0x3 /* section with only 4 byte literals */
#define  S_8BYTE_LITERALS  0x4 /* section with only 8 byte literals */
#define  S_LITERAL_POINTERS  0x5 /* section with only pointers to */

/*  literals */

/*
 * For the two types of symbol pointers sections and the symbol stubs section
 * they have indirect symbol table entries.  For each of the entries in the
 * section the indirect symbol table entries, in corresponding order in the
 * indirect symbol table, start at the index stored in the reserved1 field
 * of the section structure.  Since the indirect symbol table entries
 * correspond to the entries in the section the number of indirect symbol table
 * entries is inferred from the size of the section divided by the size of the
 * entries in the section.  For symbol pointers sections the size of the entries
 * in the section is 4 bytes and for symbol stubs sections the byte size of the
 * stubs is stored in the reserved2 field of the section structure.
 */
#define  S_NON_LAZY_SYMBOL_POINTERS  0x6 /* section with only non-lazy
                                           symbol pointers */
#define  S_LAZY_SYMBOL_POINTERS    0x7 /* section with only lazy symbol
                                         pointers */
#define  S_SYMBOL_STUBS      0x8 /* section with only symbol
                                   stubs, byte size of stub in
                                   the reserved2 field */
#define  S_MOD_INIT_FUNC_POINTERS  0x9 /* section with only function
                                         pointers for initialization */
#define  S_MOD_TERM_FUNC_POINTERS  0xa /* section with only function
                                         pointers for termination */
#define  S_COALESCED      0xb /* section contains symbols that
                               are to be coalesced */
#define  S_GB_ZEROFILL      0xc /* zero fill on demand section
                                 (that can be larger than 4
                                 gigabytes) */
#define  S_INTERPOSING      0xd /* section with only pairs of
                                 function pointers for
                                 interposing */
#define  S_16BYTE_LITERALS    0xe /* section with only 16 byte
                                   literals */
#define  S_DTRACE_DOF      0xf /* section contains
                                 DTrace Object Format */
#define  S_LAZY_DYLIB_SYMBOL_POINTERS  0x10  /* section with only lazy
                                               symbol pointers to lazy
                                               loaded dylibs */

/*
 * Section types to support thread local variables
 */
#define S_THREAD_LOCAL_REGULAR                   0x11 /* template of initial
                                                         values for TLVs */
#define S_THREAD_LOCAL_ZEROFILL                  0x12 /* template of initial
                                                         values for TLVs */
#define S_THREAD_LOCAL_VARIABLES                 0x13 /* TLV descriptors */
#define S_THREAD_LOCAL_VARIABLE_POINTERS         0x14 /* pointers to TLV
                                                         descriptors */
#define S_THREAD_LOCAL_INIT_FUNCTION_POINTERS    0x15 /* functions to call
                                                         to initialize TLV
                                                         values */

/*
 * Constants for the section attributes part of the flags field of a section
 * structure.
 */
#define SECTION_ATTRIBUTES_USR   0xff000000 /* User setable attributes */
#define S_ATTR_PURE_INSTRUCTIONS 0x80000000 /* section contains only true
                                               machine instructions */
#define S_ATTR_NO_TOC      0x40000000 /* section contains coalesced
                                         symbols that are not to be
                                         in a ranlib table of
                                         contents */
#define S_ATTR_STRIP_STATIC_SYMS 0x20000000 /* ok to strip static symbols
                                               in this section in files
                                               with the MH_DYLDLINK flag */
#define S_ATTR_NO_DEAD_STRIP   0x10000000 /* no dead stripping */
#define S_ATTR_LIVE_SUPPORT   0x08000000 /* blocks are live if they
                                           reference live blocks */
#define S_ATTR_SELF_MODIFYING_CODE 0x04000000 /* Used with i386 code stubs
                                                 written on by dyld */

/*
 * If a segment contains any sections marked with S_ATTR_DEBUG then all
 * sections in that segment must have this attribute.  No section other than
 * a section marked with this attribute may reference the contents of this
 * section.  A section with this attribute may contain no symbols and must have
 * a section type S_REGULAR.  The static linker will not copy section contents
 * from sections with this attribute into its output file.  These sections
 * generally contain DWARF debugging info.
 */
#define  S_ATTR_DEBUG     0x02000000 /* a debug section */
#define SECTION_ATTRIBUTES_SYS   0x00ffff00 /* system setable attributes */
#define S_ATTR_SOME_INSTRUCTIONS 0x00000400 /* section contains some
                                               machine instructions */
#define S_ATTR_EXT_RELOC   0x00000200 /* section has external
                                         relocation entries */
#define S_ATTR_LOC_RELOC   0x00000100 /* section has local
                                         relocation entries */

/*
 * The names of segments and sections in them are mostly meaningless to the
 * link-editor.  But there are few things to support traditional UNIX
 * executables that require the link-editor and assembler to use some names
 * agreed upon by convention.
 *
 * The initial protection of the "__TEXT" segment has write protection turned
 * off (not writeable).
 *
 * The link-editor will allocate common symbols at the end of the "__common"
 * section in the "__DATA" segment.  It will create the section and segment
 * if needed.
 */

/* The currently known segment names and the section names in those segments */

#define  SEG_PAGEZERO  "__PAGEZERO"  /* the pagezero segment which has no */

/* protections and catches NULL */

/* references for MH_EXECUTE files */

#define  SEG_TEXT  "__TEXT"  /* the tradition UNIX text segment */
#define  SECT_TEXT  "__text"  /* the real text part of the text */

/* section no headers, and no padding */
#define SECT_FVMLIB_INIT0 "__fvmlib_init0"  /* the fvmlib initialization */

/*  section */
#define SECT_FVMLIB_INIT1 "__fvmlib_init1"  /* the section following the */

/*  fvmlib initialization */

/*  section */

#define  SEG_DATA  "__DATA"  /* the tradition UNIX data segment */
#define  SECT_DATA  "__data"  /* the real initialized data section */

/* no padding, no bss overlap */
#define  SECT_BSS  "__bss" /* the real uninitialized data section */

/* no padding */
#define SECT_COMMON  "__common"  /* the section common symbols are */

/* allocated in by the link editor */

#define  SEG_OBJC  "__OBJC"  /* objective-C runtime segment */
#define SECT_OBJC_SYMBOLS "__symbol_table"  /* symbol table */
#define SECT_OBJC_MODULES "__module_info" /* module information */
#define SECT_OBJC_STRINGS "__selector_strs" /* string table */
#define SECT_OBJC_REFS "__selector_refs"  /* string table */

#define  SEG_ICON   "__ICON" /* the icon segment */
#define  SECT_ICON_HEADER "__header" /* the icon headers */
#define  SECT_ICON_TIFF   "__tiff" /* the icons in tiff format */

#define  SEG_LINKEDIT  "__LINKEDIT"  /* the segment containing all structs */

/* created and maintained by the link */

/* editor.  Created with -seglinkedit */

/* option to ld(1) for MH_EXECUTE and */

/* FVMLIB file types only */

#define SEG_UNIXSTACK  "__UNIXSTACK" /* the unix stack segment */

#define SEG_IMPORT  "__IMPORT"  /* the segment for the self (dyld) */

/* modifing code stubs that has read, */

/* write and execute permissions */

/*
 * Fixed virtual memory shared libraries are identified by two things.  The
 * target pathname (the name of the library as found for execution), and the
 * minor version number.  The address of where the headers are loaded is in
 * header_addr. (THIS IS OBSOLETE and no longer supported).
 */
struct fvmlib {
  union lc_str name;            /* library's target pathname */
  uint32_t minor_version;       /* library's minor version number */
  uint32_t header_addr;         /* library's header address */
};

/*
 * A fixed virtual shared library (filetype == MH_FVMLIB in the mach header)
 * contains a fvmlib_command (cmd == LC_IDFVMLIB) to identify the library.
 * An object that uses a fixed virtual shared library also contains a
 * fvmlib_command (cmd == LC_LOADFVMLIB) for each library it uses.
 * (THIS IS OBSOLETE and no longer supported).
 */
struct fvmlib_command {
  uint32_t cmd;                 /* LC_IDFVMLIB or LC_LOADFVMLIB */
  uint32_t cmdsize;             /* includes pathname string */
  struct fvmlib fvmlib;         /* the library identification */
};

/*
 * Dynamicly linked shared libraries are identified by two things.  The
 * pathname (the name of the library as found for execution), and the
 * compatibility version number.  The pathname must match and the compatibility
 * number in the user of the library must be greater than or equal to the
 * library being used.  The time stamp is used to record the time a library was
 * built and copied into user so it can be use to determined if the library used
 * at runtime is exactly the same as used to built the program.
 */
struct dylib {
  union lc_str name;            /* library's path name */
  uint32_t timestamp;           /* library's build time stamp */
  uint32_t current_version;     /* library's current version number */
  uint32_t compatibility_version; /* library's compatibility vers number */
};

/*
 * A dynamically linked shared library (filetype == MH_DYLIB in the mach header)
 * contains a dylib_command (cmd == LC_ID_DYLIB) to identify the library.
 * An object that uses a dynamically linked shared library also contains a
 * dylib_command (cmd == LC_LOAD_DYLIB, LC_LOAD_WEAK_DYLIB, or
 * LC_REEXPORT_DYLIB) for each library it uses.
 */
struct dylib_command {
  uint32_t cmd;                 /* LC_ID_DYLIB, LC_LOAD_{,WEAK_}DYLIB,
                                   LC_REEXPORT_DYLIB */
  uint32_t cmdsize;             /* includes pathname string */
  struct dylib dylib;           /* the library identification */
};

/*
 * A dynamically linked shared library may be a subframework of an umbrella
 * framework.  If so it will be linked with "-umbrella umbrella_name" where
 * Where "umbrella_name" is the name of the umbrella framework. A subframework
 * can only be linked against by its umbrella framework or other subframeworks
 * that are part of the same umbrella framework.  Otherwise the static link
 * editor produces an error and states to link against the umbrella framework.
 * The name of the umbrella framework for subframeworks is recorded in the
 * following structure.
 */
struct sub_framework_command {
  uint32_t cmd;                 /* LC_SUB_FRAMEWORK */
  uint32_t cmdsize;             /* includes umbrella string */
  union lc_str umbrella;        /* the umbrella framework name */
};

/*
 * For dynamically linked shared libraries that are subframework of an umbrella
 * framework they can allow clients other than the umbrella framework or other
 * subframeworks in the same umbrella framework.  To do this the subframework
 * is built with "-allowable_client client_name" and an LC_SUB_CLIENT load
 * command is created for each -allowable_client flag.  The client_name is
 * usually a framework name.  It can also be a name used for bundles clients
 * where the bundle is built with "-client_name client_name".
 */
struct sub_client_command {
  uint32_t cmd;                 /* LC_SUB_CLIENT */
  uint32_t cmdsize;             /* includes client string */
  union lc_str client;          /* the client name */
};

/*
 * A dynamically linked shared library may be a sub_umbrella of an umbrella
 * framework.  If so it will be linked with "-sub_umbrella umbrella_name" where
 * Where "umbrella_name" is the name of the sub_umbrella framework.  When
 * staticly linking when -twolevel_namespace is in effect a twolevel namespace
 * umbrella framework will only cause its subframeworks and those frameworks
 * listed as sub_umbrella frameworks to be implicited linked in.  Any other
 * dependent dynamic libraries will not be linked it when -twolevel_namespace
 * is in effect.  The primary library recorded by the static linker when
 * resolving a symbol in these libraries will be the umbrella framework.
 * Zero or more sub_umbrella frameworks may be use by an umbrella framework.
 * The name of a sub_umbrella framework is recorded in the following structure.
 */
struct sub_umbrella_command {
  uint32_t cmd;                 /* LC_SUB_UMBRELLA */
  uint32_t cmdsize;             /* includes sub_umbrella string */
  union lc_str sub_umbrella;    /* the sub_umbrella framework name */
};

/*
 * A dynamically linked shared library may be a sub_library of another shared
 * library.  If so it will be linked with "-sub_library library_name" where
 * Where "library_name" is the name of the sub_library shared library.  When
 * staticly linking when -twolevel_namespace is in effect a twolevel namespace
 * shared library will only cause its subframeworks and those frameworks
 * listed as sub_umbrella frameworks and libraries listed as sub_libraries to
 * be implicited linked in.  Any other dependent dynamic libraries will not be
 * linked it when -twolevel_namespace is in effect.  The primary library
 * recorded by the static linker when resolving a symbol in these libraries
 * will be the umbrella framework (or dynamic library). Zero or more sub_library
 * shared libraries may be use by an umbrella framework or (or dynamic library).
 * The name of a sub_library framework is recorded in the following structure.
 * For example /usr/lib/libobjc_profile.A.dylib would be recorded as "libobjc".
 */
struct sub_library_command {
  uint32_t cmd;                 /* LC_SUB_LIBRARY */
  uint32_t cmdsize;             /* includes sub_library string */
  union lc_str sub_library;     /* the sub_library name */
};

/*
 * A program (filetype == MH_EXECUTE) that is
 * prebound to its dynamic libraries has one of these for each library that
 * the static linker used in prebinding.  It contains a bit vector for the
 * modules in the library.  The bits indicate which modules are bound (1) and
 * which are not (0) from the library.  The bit for module 0 is the low bit
 * of the first byte.  So the bit for the Nth module is:
 * (linked_modules[N/8] >> N%8) & 1
 */
struct prebound_dylib_command {
  uint32_t cmd;                 /* LC_PREBOUND_DYLIB */
  uint32_t cmdsize;             /* includes strings */
  union lc_str name;            /* library's path name */
  uint32_t nmodules;            /* number of modules in library */
  union lc_str linked_modules;  /* bit vector of linked modules */
};

/*
 * A program that uses a dynamic linker contains a dylinker_command to identify
 * the name of the dynamic linker (LC_LOAD_DYLINKER).  And a dynamic linker
 * contains a dylinker_command to identify the dynamic linker (LC_ID_DYLINKER).
 * A file can have at most one of these.
 * This struct is also used for the LC_DYLD_ENVIRONMENT load command and
 * contains string for dyld to treat like environment variable.
 */
struct dylinker_command {
  uint32_t cmd;                 /* LC_ID_DYLINKER, LC_LOAD_DYLINKER or
                                   LC_DYLD_ENVIRONMENT */
  uint32_t cmdsize;             /* includes pathname string */
  union lc_str name;            /* dynamic linker's path name */
};

/*
 * Thread commands contain machine-specific data structures suitable for
 * use in the thread state primitives.  The machine specific data structures
 * follow the struct thread_command as follows.
 * Each flavor of machine specific data structure is preceded by an unsigned
 * long constant for the flavor of that data structure, an uint32_t
 * that is the count of longs of the size of the state data structure and then
 * the state data structure follows.  This triple may be repeated for many
 * flavors.  The constants for the flavors, counts and state data structure
 * definitions are expected to be in the header file <machine/thread_status.h>.
 * These machine specific data structures sizes must be multiples of
 * 4 bytes  The cmdsize reflects the total size of the thread_command
 * and all of the sizes of the constants for the flavors, counts and state
 * data structures.
 *
 * For executable objects that are unix processes there will be one
 * thread_command (cmd == LC_UNIXTHREAD) created for it by the link-editor.
 * This is the same as a LC_THREAD, except that a stack is automatically
 * created (based on the shell's limit for the stack size).  Command arguments
 * and environment variables are copied onto that stack.
 */
struct thread_command {
  uint32_t cmd;                 /* LC_THREAD or  LC_UNIXTHREAD */
  uint32_t cmdsize;             /* total size of this command */
  /* uint32_t flavor       flavor of thread state */
  /* uint32_t count      count of longs in thread state */
  /* struct XXX_thread_state state   thread state for this flavor */
  /* ... */
};

/*
 * The routines command contains the address of the dynamic shared library
 * initialization routine and an index into the module table for the module
 * that defines the routine.  Before any modules are used from the library the
 * dynamic linker fully binds the module that defines the initialization routine
 * and then calls it.  This gets called before any module initialization
 * routines (used for C++ static constructors) in the library.
 */
struct routines_command {       /* for 32-bit architectures */
  uint32_t cmd;                 /* LC_ROUTINES */
  uint32_t cmdsize;             /* total size of this command */
  uint32_t init_address;        /* address of initialization routine */
  uint32_t init_module;         /* index into the module table that */
  /*  the init routine is defined in */
  uint32_t reserved1;
  uint32_t reserved2;
  uint32_t reserved3;
  uint32_t reserved4;
  uint32_t reserved5;
  uint32_t reserved6;
};

/*
 * The 64-bit routines command.  Same use as above.
 */
struct routines_command_64 {    /* for 64-bit architectures */
  uint32_t cmd;                 /* LC_ROUTINES_64 */
  uint32_t cmdsize;             /* total size of this command */
  uint64_t init_address;        /* address of initialization routine */
  uint64_t init_module;         /* index into the module table that */
  /*  the init routine is defined in */
  uint64_t reserved1;
  uint64_t reserved2;
  uint64_t reserved3;
  uint64_t reserved4;
  uint64_t reserved5;
  uint64_t reserved6;
};

/*
 * The symtab_command contains the offsets and sizes of the link-edit 4.3BSD
 * "stab" style symbol table information as described in the header files
 * <nlist.h> and <stab.h>.
 */
struct symtab_command {
  uint32_t cmd;                 /* LC_SYMTAB */
  uint32_t cmdsize;             /* sizeof(struct symtab_command) */
  uint32_t symoff;              /* symbol table offset */
  uint32_t nsyms;               /* number of symbol table entries */
  uint32_t stroff;              /* string table offset */
  uint32_t strsize;             /* string table size in bytes */
};

/*
 * This is the second set of the symbolic information which is used to support
 * the data structures for the dynamically link editor.
 *
 * The original set of symbolic information in the symtab_command which contains
 * the symbol and string tables must also be present when this load command is
 * present.  When this load command is present the symbol table is organized
 * into three groups of symbols:
 *  local symbols (static and debugging symbols) - grouped by module
 *  defined external symbols - grouped by module (sorted by name if not lib)
 *  undefined external symbols (sorted by name if MH_BINDATLOAD is not set,
 *                 and in order the were seen by the static
 *            linker if MH_BINDATLOAD is set)
 * In this load command there are offsets and counts to each of the three groups
 * of symbols.
 *
 * This load command contains a the offsets and sizes of the following new
 * symbolic information tables:
 *  table of contents
 *  module table
 *  reference symbol table
 *  indirect symbol table
 * The first three tables above (the table of contents, module table and
 * reference symbol table) are only present if the file is a dynamically linked
 * shared library.  For executable and object modules, which are files
 * containing only one module, the information that would be in these three
 * tables is determined as follows:
 *   table of contents - the defined external symbols are sorted by name
 *  module table - the file contains only one module so everything in the
 *           file is part of the module.
 *  reference symbol table - is the defined and undefined external symbols
 *
 * For dynamically linked shared library files this load command also contains
 * offsets and sizes to the pool of relocation entries for all sections
 * separated into two groups:
 *  external relocation entries
 *  local relocation entries
 * For executable and object modules the relocation entries continue to hang
 * off the section structures.
 */
struct dysymtab_command {
  uint32_t cmd;                 /* LC_DYSYMTAB */
  uint32_t cmdsize;             /* sizeof(struct dysymtab_command) */

  /*
   * The symbols indicated by symoff and nsyms of the LC_SYMTAB load command
   * are grouped into the following three groups:
   *    local symbols (further grouped by the module they are from)
   *    defined external symbols (further grouped by the module they are from)
   *    undefined symbols
   *
   * The local symbols are used only for debugging.  The dynamic binding
   * process may have to use them to indicate to the debugger the local
   * symbols for a module that is being bound.
   *
   * The last two groups are used by the dynamic binding process to do the
   * binding (indirectly through the module table and the reference symbol
   * table when this is a dynamically linked shared library file).
   */
  uint32_t ilocalsym;           /* index to local symbols */
  uint32_t nlocalsym;           /* number of local symbols */

  uint32_t iextdefsym;          /* index to externally defined symbols */
  uint32_t nextdefsym;          /* number of externally defined symbols */

  uint32_t iundefsym;           /* index to undefined symbols */
  uint32_t nundefsym;           /* number of undefined symbols */

  /*
   * For the for the dynamic binding process to find which module a symbol
   * is defined in the table of contents is used (analogous to the ranlib
   * structure in an archive) which maps defined external symbols to modules
   * they are defined in.  This exists only in a dynamically linked shared
   * library file.  For executable and object modules the defined external
   * symbols are sorted by name and is use as the table of contents.
   */
  uint32_t tocoff;              /* file offset to table of contents */
  uint32_t ntoc;                /* number of entries in table of contents */

  /*
   * To support dynamic binding of "modules" (whole object files) the symbol
   * table must reflect the modules that the file was created from.  This is
   * done by having a module table that has indexes and counts into the merged
   * tables for each module.  The module structure that these two entries
   * refer to is described below.  This exists only in a dynamically linked
   * shared library file.  For executable and object modules the file only
   * contains one module so everything in the file belongs to the module.
   */
  uint32_t modtaboff;           /* file offset to module table */
  uint32_t nmodtab;             /* number of module table entries */

  /*
   * To support dynamic module binding the module structure for each module
   * indicates the external references (defined and undefined) each module
   * makes.  For each module there is an offset and a count into the
   * reference symbol table for the symbols that the module references.
   * This exists only in a dynamically linked shared library file.  For
   * executable and object modules the defined external symbols and the
   * undefined external symbols indicates the external references.
   */
  uint32_t extrefsymoff;        /* offset to referenced symbol table */
  uint32_t nextrefsyms;         /* number of referenced symbol table entries */

  /*
   * The sections that contain "symbol pointers" and "routine stubs" have
   * indexes and (implied counts based on the size of the section and fixed
   * size of the entry) into the "indirect symbol" table for each pointer
   * and stub.  For every section of these two types the index into the
   * indirect symbol table is stored in the section header in the field
   * reserved1.  An indirect symbol table entry is simply a 32bit index into
   * the symbol table to the symbol that the pointer or stub is referring to.
   * The indirect symbol table is ordered to match the entries in the section.
   */
  uint32_t indirectsymoff;      /* file offset to the indirect symbol table */
  uint32_t nindirectsyms;       /* number of indirect symbol table entries */

  /*
   * To support relocating an individual module in a library file quickly the
   * external relocation entries for each module in the library need to be
   * accessed efficiently.  Since the relocation entries can't be accessed
   * through the section headers for a library file they are separated into
   * groups of local and external entries further grouped by module.  In this
   * case the presents of this load command who's extreloff, nextrel,
   * locreloff and nlocrel fields are non-zero indicates that the relocation
   * entries of non-merged sections are not referenced through the section
   * structures (and the reloff and nreloc fields in the section headers are
   * set to zero).
   *
   * Since the relocation entries are not accessed through the section headers
   * this requires the r_address field to be something other than a section
   * offset to identify the item to be relocated.  In this case r_address is
   * set to the offset from the vmaddr of the first LC_SEGMENT command.
   * For MH_SPLIT_SEGS images r_address is set to the the offset from the
   * vmaddr of the first read-write LC_SEGMENT command.
   *
   * The relocation entries are grouped by module and the module table
   * entries have indexes and counts into them for the group of external
   * relocation entries for that the module.
   *
   * For sections that are merged across modules there must not be any
   * remaining external relocation entries for them (for merged sections
   * remaining relocation entries must be local).
   */
  uint32_t extreloff;           /* offset to external relocation entries */
  uint32_t nextrel;             /* number of external relocation entries */

  /*
   * All the local relocation entries are grouped together (they are not
   * grouped by their module since they are only used if the object is moved
   * from it staticly link edited address).
   */
  uint32_t locreloff;           /* offset to local relocation entries */
  uint32_t nlocrel;             /* number of local relocation entries */

};

/*
 * An indirect symbol table entry is simply a 32bit index into the symbol table
 * to the symbol that the pointer or stub is refering to.  Unless it is for a
 * non-lazy symbol pointer section for a defined symbol which strip(1) as
 * removed.  In which case it has the value INDIRECT_SYMBOL_LOCAL.  If the
 * symbol was also absolute INDIRECT_SYMBOL_ABS is or'ed with that.
 */
#define INDIRECT_SYMBOL_LOCAL  0x80000000
#define INDIRECT_SYMBOL_ABS  0x40000000

/* a table of contents entry */
struct dylib_table_of_contents {
  uint32_t symbol_index;        /* the defined external symbol
                                   (index into the symbol table) */
  uint32_t module_index;        /* index into the module table this symbol
                                   is defined in */
};

/* a module table entry */
struct dylib_module {
  uint32_t module_name;         /* the module name (index into string table) */

  uint32_t iextdefsym;          /* index into externally defined symbols */
  uint32_t nextdefsym;          /* number of externally defined symbols */
  uint32_t irefsym;             /* index into reference symbol table */
  uint32_t nrefsym;             /* number of reference symbol table entries */
  uint32_t ilocalsym;           /* index into symbols for local symbols */
  uint32_t nlocalsym;           /* number of local symbols */

  uint32_t iextrel;             /* index into external relocation entries */
  uint32_t nextrel;             /* number of external relocation entries */

  uint32_t iinit_iterm;         /* low 16 bits are the index into the init
                                   section, high 16 bits are the index into
                                   the term section */
  uint32_t ninit_nterm;         /* low 16 bits are the number of init section
                                   entries, high 16 bits are the number of
                                   term section entries */

    uint32_t                    /* for this module address of the start of */
    objc_module_info_addr;      /*  the (__OBJC,__module_info) section */
    uint32_t                    /* for this module size of */
    objc_module_info_size;      /*  the (__OBJC,__module_info) section */
};

/* a 64-bit module table entry */
struct dylib_module_64 {
  uint32_t module_name;         /* the module name (index into string table) */

  uint32_t iextdefsym;          /* index into externally defined symbols */
  uint32_t nextdefsym;          /* number of externally defined symbols */
  uint32_t irefsym;             /* index into reference symbol table */
  uint32_t nrefsym;             /* number of reference symbol table entries */
  uint32_t ilocalsym;           /* index into symbols for local symbols */
  uint32_t nlocalsym;           /* number of local symbols */

  uint32_t iextrel;             /* index into external relocation entries */
  uint32_t nextrel;             /* number of external relocation entries */

  uint32_t iinit_iterm;         /* low 16 bits are the index into the init
                                   section, high 16 bits are the index into
                                   the term section */
  uint32_t ninit_nterm;         /* low 16 bits are the number of init section
                                   entries, high 16 bits are the number of
                                   term section entries */

    uint32_t                    /* for this module size of */
    objc_module_info_size;      /*  the (__OBJC,__module_info) section */
    uint64_t                    /* for this module address of the start of */
    objc_module_info_addr;      /*  the (__OBJC,__module_info) section */
};

/*
 * The entries in the reference symbol table are used when loading the module
 * (both by the static and dynamic link editors) and if the module is unloaded
 * or replaced.  Therefore all external symbols (defined and undefined) are
 * listed in the module's reference table.  The flags describe the type of
 * reference that is being made.  The constants for the flags are defined in
 * <mach-o/nlist.h> as they are also used for symbol table entries.
 */
struct dylib_reference {
  uint32_t isym:24,             /* index into the symbol table */
    flags:8;                    /* flags to indicate the type of reference */
};

/*
 * The twolevel_hints_command contains the offset and number of hints in the
 * two-level namespace lookup hints table.
 */
struct twolevel_hints_command {
  uint32_t cmd;                 /* LC_TWOLEVEL_HINTS */
  uint32_t cmdsize;             /* sizeof(struct twolevel_hints_command) */
  uint32_t offset;              /* offset to the hint table */
  uint32_t nhints;              /* number of hints in the hint table */
};

/*
 * The entries in the two-level namespace lookup hints table are twolevel_hint
 * structs.  These provide hints to the dynamic link editor where to start
 * looking for an undefined symbol in a two-level namespace image.  The
 * isub_image field is an index into the sub-images (sub-frameworks and
 * sub-umbrellas list) that made up the two-level image that the undefined
 * symbol was found in when it was built by the static link editor.  If
 * isub-image is 0 the the symbol is expected to be defined in library and not
 * in the sub-images.  If isub-image is non-zero it is an index into the array
 * of sub-images for the umbrella with the first index in the sub-images being
 * 1. The array of sub-images is the ordered list of sub-images of the umbrella
 * that would be searched for a symbol that has the umbrella recorded as its
 * primary library.  The table of contents index is an index into the
 * library's table of contents.  This is used as the starting point of the
 * binary search or a directed linear search.
 */
struct twolevel_hint {
  uint32_t isub_image:8,        /* index into the sub images */
  itoc:24;                      /* index into the table of contents */
};

/*
 * The prebind_cksum_command contains the value of the original check sum for
 * prebound files or zero.  When a prebound file is first created or modified
 * for other than updating its prebinding information the value of the check sum
 * is set to zero.  When the file has it prebinding re-done and if the value of
 * the check sum is zero the original check sum is calculated and stored in
 * cksum field of this load command in the output file.  If when the prebinding
 * is re-done and the cksum field is non-zero it is left unchanged from the
 * input file.
 */
struct prebind_cksum_command {
  uint32_t cmd;                 /* LC_PREBIND_CKSUM */
  uint32_t cmdsize;             /* sizeof(struct prebind_cksum_command) */
  uint32_t cksum;               /* the check sum or zero */
};

/*
 * The uuid load command contains a single 128-bit unique random number that
 * identifies an object produced by the static link editor.
 */
struct uuid_command {
  uint32_t cmd;                 /* LC_UUID */
  uint32_t cmdsize;             /* sizeof(struct uuid_command) */
  uint8_t uuid[16];             /* the 128-bit uuid */
};

/*
 * The rpath_command contains a path which at runtime should be added to
 * the current run path used to find @rpath prefixed dylibs.
 */
struct rpath_command {
  uint32_t cmd;                 /* LC_RPATH */
  uint32_t cmdsize;             /* includes string */
  union lc_str path;            /* path to add to run path */
};

/*
 * The linkedit_data_command contains the offsets and sizes of a blob
 * of data in the __LINKEDIT segment.
 */
struct linkedit_data_command {
  uint32_t cmd;                 /* LC_CODE_SIGNATURE, LC_SEGMENT_SPLIT_INFO,
                                   LC_FUNCTION_STARTS, LC_DATA_IN_CODE,
                                   or LC_DYLIB_CODE_SIGN_DRS */
  uint32_t cmdsize;             /* sizeof(struct linkedit_data_command) */
  uint32_t dataoff;             /* file offset of data in __LINKEDIT segment */
  uint32_t datasize;            /* file size of data in __LINKEDIT segment  */
};

/*
 * The encryption_info_command contains the file offset and size of an
 * of an encrypted segment.
 */
struct encryption_info_command {
  uint32_t cmd;                 /* LC_ENCRYPTION_INFO */
  uint32_t cmdsize;             /* sizeof(struct encryption_info_command) */
  uint32_t cryptoff;            /* file offset of encrypted range */
  uint32_t cryptsize;           /* file size of encrypted range */
  uint32_t cryptid;             /* which enryption system,
                                   0 means not-encrypted yet */
};

/*
 * The version_min_command contains the min OS version on which this
 * binary was built to run.
 */
struct version_min_command {
  uint32_t cmd;                 /* LC_VERSION_MIN_MACOSX or
                                   LC_VERSION_MIN_IPHONEOS  */
  uint32_t cmdsize;             /* sizeof(struct min_version_command) */
  uint32_t version;             /* X.Y.Z is encoded in nibbles xxxx.yy.zz */
  uint32_t sdk;                 /* X.Y.Z is encoded in nibbles xxxx.yy.zz */
};

/*
 * The dyld_info_command contains the file offsets and sizes of
 * the new compressed form of the information dyld needs to
 * load the image.  This information is used by dyld on Mac OS X
 * 10.6 and later.  All information pointed to by this command
 * is encoded using byte streams, so no endian swapping is needed
 * to interpret it.
 */
struct dyld_info_command {
  uint32_t cmd;                 /* LC_DYLD_INFO or LC_DYLD_INFO_ONLY */
  uint32_t cmdsize;             /* sizeof(struct dyld_info_command) */

  /*
   * Dyld rebases an image whenever dyld loads it at an address different
   * from its preferred address.  The rebase information is a stream
   * of byte sized opcodes whose symbolic names start with REBASE_OPCODE_.
   * Conceptually the rebase information is a table of tuples:
   *    <seg-index, seg-offset, type>
   * The opcodes are a compressed way to encode the table by only
   * encoding when a column changes.  In addition simple patterns
   * like "every n'th offset for m times" can be encoded in a few
   * bytes.
   */
  uint32_t rebase_off;          /* file offset to rebase info  */
  uint32_t rebase_size;         /* size of rebase info   */

  /*
   * Dyld binds an image during the loading process, if the image
   * requires any pointers to be initialized to symbols in other images.
   * The bind information is a stream of byte sized
   * opcodes whose symbolic names start with BIND_OPCODE_.
   * Conceptually the bind information is a table of tuples:
   *    <seg-index, seg-offset, type, symbol-library-ordinal, symbol-name, addend>
   * The opcodes are a compressed way to encode the table by only
   * encoding when a column changes.  In addition simple patterns
   * like for runs of pointers initialzed to the same value can be
   * encoded in a few bytes.
   */
  uint32_t bind_off;            /* file offset to binding info   */
  uint32_t bind_size;           /* size of binding info  */

  /*
   * Some C++ programs require dyld to unique symbols so that all
   * images in the process use the same copy of some code/data.
   * This step is done after binding. The content of the weak_bind
   * info is an opcode stream like the bind_info.  But it is sorted
   * alphabetically by symbol name.  This enable dyld to walk
   * all images with weak binding information in order and look
   * for collisions.  If there are no collisions, dyld does
   * no updating.  That means that some fixups are also encoded
   * in the bind_info.  For instance, all calls to "operator new"
   * are first bound to libstdc++.dylib using the information
   * in bind_info.  Then if some image overrides operator new
   * that is detected when the weak_bind information is processed
   * and the call to operator new is then rebound.
   */
  uint32_t weak_bind_off;       /* file offset to weak binding info   */
  uint32_t weak_bind_size;      /* size of weak binding info  */

  /*
   * Some uses of external symbols do not need to be bound immediately.
   * Instead they can be lazily bound on first use.  The lazy_bind
   * are contains a stream of BIND opcodes to bind all lazy symbols.
   * Normal use is that dyld ignores the lazy_bind section when
   * loading an image.  Instead the static linker arranged for the
   * lazy pointer to initially point to a helper function which
   * pushes the offset into the lazy_bind area for the symbol
   * needing to be bound, then jumps to dyld which simply adds
   * the offset to lazy_bind_off to get the information on what
   * to bind.
   */
  uint32_t lazy_bind_off;       /* file offset to lazy binding info */
  uint32_t lazy_bind_size;      /* size of lazy binding infs */

  /*
   * The symbols exported by a dylib are encoded in a trie.  This
   * is a compact representation that factors out common prefixes.
   * It also reduces LINKEDIT pages in RAM because it encodes all
   * information (name, address, flags) in one small, contiguous range.
   * The export area is a stream of nodes.  The first node sequentially
   * is the start node for the trie.
   *
   * Nodes for a symbol start with a uleb128 that is the length of
   * the exported symbol information for the string so far.
   * If there is no exported symbol, the node starts with a zero byte.
   * If there is exported info, it follows the length.
   *
   * First is a uleb128 containing flags. Normally, it is followed by
   * a uleb128 encoded offset which is location of the content named
   * by the symbol from the mach_header for the image.  If the flags
   * is EXPORT_SYMBOL_FLAGS_REEXPORT, then following the flags is
   * a uleb128 encoded library ordinal, then a zero terminated
   * UTF8 string.  If the string is zero length, then the symbol
   * is re-export from the specified dylib with the same name.
   * If the flags is EXPORT_SYMBOL_FLAGS_STUB_AND_RESOLVER, then following
   * the flags is two uleb128s: the stub offset and the resolver offset.
   * The stub is used by non-lazy pointers.  The resolver is used
   * by lazy pointers and must be called to get the actual address to use.
   *
   * After the optional exported symbol information is a byte of
   * how many edges (0-255) that this node has leaving it,
   * followed by each edge.
   * Each edge is a zero terminated UTF8 of the addition chars
   * in the symbol, followed by a uleb128 offset for the node that
   * edge points to.
   *
   */
  uint32_t export_off;          /* file offset to lazy binding info */
  uint32_t export_size;         /* size of lazy binding infs */
};

/*
 * The following are used to encode rebasing information
 */
#define REBASE_TYPE_POINTER          1
#define REBASE_TYPE_TEXT_ABSOLUTE32        2
#define REBASE_TYPE_TEXT_PCREL32        3

#define REBASE_OPCODE_MASK          0xF0
#define REBASE_IMMEDIATE_MASK          0x0F
#define REBASE_OPCODE_DONE          0x00
#define REBASE_OPCODE_SET_TYPE_IMM        0x10
#define REBASE_OPCODE_SET_SEGMENT_AND_OFFSET_ULEB    0x20
#define REBASE_OPCODE_ADD_ADDR_ULEB        0x30
#define REBASE_OPCODE_ADD_ADDR_IMM_SCALED      0x40
#define REBASE_OPCODE_DO_REBASE_IMM_TIMES      0x50
#define REBASE_OPCODE_DO_REBASE_ULEB_TIMES      0x60
#define REBASE_OPCODE_DO_REBASE_ADD_ADDR_ULEB      0x70
#define REBASE_OPCODE_DO_REBASE_ULEB_TIMES_SKIPPING_ULEB  0x80

/*
 * The following are used to encode binding information
 */
#define BIND_TYPE_POINTER          1
#define BIND_TYPE_TEXT_ABSOLUTE32        2
#define BIND_TYPE_TEXT_PCREL32          3

#define BIND_SPECIAL_DYLIB_SELF           0
#define BIND_SPECIAL_DYLIB_MAIN_EXECUTABLE      -1
#define BIND_SPECIAL_DYLIB_FLAT_LOOKUP        -2

#define BIND_SYMBOL_FLAGS_WEAK_IMPORT        0x1
#define BIND_SYMBOL_FLAGS_NON_WEAK_DEFINITION      0x8

#define BIND_OPCODE_MASK          0xF0
#define BIND_IMMEDIATE_MASK          0x0F
#define BIND_OPCODE_DONE          0x00
#define BIND_OPCODE_SET_DYLIB_ORDINAL_IMM      0x10
#define BIND_OPCODE_SET_DYLIB_ORDINAL_ULEB      0x20
#define BIND_OPCODE_SET_DYLIB_SPECIAL_IMM      0x30
#define BIND_OPCODE_SET_SYMBOL_TRAILING_FLAGS_IMM    0x40
#define BIND_OPCODE_SET_TYPE_IMM        0x50
#define BIND_OPCODE_SET_ADDEND_SLEB        0x60
#define BIND_OPCODE_SET_SEGMENT_AND_OFFSET_ULEB      0x70
#define BIND_OPCODE_ADD_ADDR_ULEB        0x80
#define BIND_OPCODE_DO_BIND          0x90
#define BIND_OPCODE_DO_BIND_ADD_ADDR_ULEB      0xA0
#define BIND_OPCODE_DO_BIND_ADD_ADDR_IMM_SCALED      0xB0
#define BIND_OPCODE_DO_BIND_ULEB_TIMES_SKIPPING_ULEB    0xC0

/*
 * The following are used on the flags byte of a terminal node
 * in the export information.
 */
#define EXPORT_SYMBOL_FLAGS_KIND_MASK        0x03
#define EXPORT_SYMBOL_FLAGS_KIND_REGULAR      0x00
#define EXPORT_SYMBOL_FLAGS_KIND_THREAD_LOCAL      0x01
#define EXPORT_SYMBOL_FLAGS_WEAK_DEFINITION      0x04
#define EXPORT_SYMBOL_FLAGS_REEXPORT        0x08
#define EXPORT_SYMBOL_FLAGS_STUB_AND_RESOLVER      0x10

/*
 * The symseg_command contains the offset and size of the GNU style
 * symbol table information as described in the header file <symseg.h>.
 * The symbol roots of the symbol segments must also be aligned properly
 * in the file.  So the requirement of keeping the offsets aligned to a
 * multiple of a 4 bytes translates to the length field of the symbol
 * roots also being a multiple of a long.  Also the padding must again be
 * zeroed. (THIS IS OBSOLETE and no longer supported).
 */
struct symseg_command {
  uint32_t cmd;                 /* LC_SYMSEG */
  uint32_t cmdsize;             /* sizeof(struct symseg_command) */
  uint32_t offset;              /* symbol segment offset */
  uint32_t size;                /* symbol segment size in bytes */
};

/*
 * The ident_command contains a free format string table following the
 * ident_command structure.  The strings are null terminated and the size of
 * the command is padded out with zero bytes to a multiple of 4 bytes/
 * (THIS IS OBSOLETE and no longer supported).
 */
struct ident_command {
  uint32_t cmd;                 /* LC_IDENT */
  uint32_t cmdsize;             /* strings that follow this command */
};

/*
 * The fvmfile_command contains a reference to a file to be loaded at the
 * specified virtual address.  (Presently, this command is reserved for
 * internal use.  The kernel ignores this command when loading a program into
 * memory).
 */
struct fvmfile_command {
  uint32_t cmd;                 /* LC_FVMFILE */
  uint32_t cmdsize;             /* includes pathname string */
  union lc_str name;            /* files pathname */
  uint32_t header_addr;         /* files virtual address */
};

/*
 * The entry_point_command is a replacement for thread_command.
 * It is used for main executables to specify the location (file offset)
 * of main().  If -stack_size was used at link time, the stacksize
 * field will contain the stack size need for the main thread.
 */
struct entry_point_command {
  uint32_t cmd;                 /* LC_MAIN only used in MH_EXECUTE filetypes */
  uint32_t cmdsize;             /* 24 */
  uint64_t entryoff;            /* file (__TEXT) offset of main() */
  uint64_t stacksize;           /* if not zero, initial stack size */
};

/*
 * The source_version_command is an optional load command containing
 * the version of the sources used to build the binary.
 */
struct source_version_command {
  uint32_t cmd;                 /* LC_SOURCE_VERSION */
  uint32_t cmdsize;             /* 16 */
  uint64_t version;             /* A.B.C.D.E packed as a24.b10.c10.d10.e10 */
};

/*
 * The LC_DATA_IN_CODE load commands uses a linkedit_data_command
 * to point to an array of data_in_code_entry entries. Each entry
 * describes a range of data in a code section.  This load command
 * is only used in final linked images.
 */
struct data_in_code_entry {
  uint32_t offset;              /* from mach_header to start of data range */
  uint16_t length;              /* number of bytes in data range */
  uint16_t kind;                /* a DICE_KIND_* value  */
};

#define DICE_KIND_DATA              0x0001  /* L$start$data$...  label */
#define DICE_KIND_JUMP_TABLE8       0x0002  /* L$start$jt8$...   label */
#define DICE_KIND_JUMP_TABLE16      0x0003  /* L$start$jt16$...  label */
#define DICE_KIND_JUMP_TABLE32      0x0004  /* L$start$jt32$...  label */
#define DICE_KIND_ABS_JUMP_TABLE32  0x0005  /* L$start$jta32$... label */

/*
 * Sections of type S_THREAD_LOCAL_VARIABLES contain an array
 * of tlv_descriptor structures.
 */
struct tlv_descriptor {
  void *(
  *thunk
  ) (
  struct tlv_descriptor *
  );
  unsigned long key;
  unsigned long offset;
};

#endif /* _MACHO_LOADER_H_ */
